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Homework Help: Ball Free fall question

  1. Oct 23, 2008 #1
    1. The problem statement, all variables and given/known data
    A ball is tossed from an upper-story window of a building. The ball is given an initial velocity of 8.20 m/s at an angle of 15.0° below the horizontal. It strikes the ground 3.00 s later.
    (a) How far horizontally from the base of the building does the ball strike the ground?
    4.90wrong check mark m
    (b) Find the height from which the ball was thrown.
    wrong check mark m
    (c) How long does it take the ball to reach a point 10.0 m below the level of launching?

    2. Relevant equations
    i think the equations are r= v^2(sin2theta)/g
    h= v^2(sintheta)2/2g

    3. The attempt at a solution
    i tried pluggin in the values to get how far it travelled and the height..but im getting it wrong

    any help would be appreciated
  2. jcsd
  3. Oct 23, 2008 #2


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    Work out the velocity component downward.
    Then it's just the normal moving object equations except the initial velocity isn't zero.
  4. Oct 23, 2008 #3
    im not sure wat you mean by that

    make the velocity -8.2?
    im so confused
  5. Oct 23, 2008 #4


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    Staff Emeritus
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    You need to resolve the velocity vector into horizontal and vertical components. Then, what mgb is saying, is you consider the vertical component.
  6. Oct 23, 2008 #5
    o ok into two different components

    so they give me 8.2 m/s
    thats my resultant vector rite?

    so i just do 8.2(cos15) ??
  7. Oct 23, 2008 #6


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    Draw a diagram (triangle) - it should be obvious how much of the diagonal speed goes horizontally and how much vertically.
  8. Oct 23, 2008 #7
    alrite cool
    thanks a lot guys
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